text:
Would "Mad" Mike Hughes' steam-powered rocket have been certified airworthy by the FAA?
Daredevil 'Mad' Mike Hughes died after his homemade rocket crashed on 22 February 2020. The cause appears to be the premature deployment of the parachute used for a safe return. He was hoping to reach 5000ft.
In the U.S., Title 14, Code of Federal Regulations, Subchapter F, Part 91.7 states:

"No person may operate an aircraft unless it is in an airworthy
  condition"

The FAA defines an aircraft as "A device that is used or intended to be used for flight in the air" and has extensive information on certifying home-built or experimental aircraft. The original rationale, I presume, being that an aircraft is a danger not only to its occupants but people on the ground too.
They also say

the owner or operator of an aircraft is primarily responsible for
  maintaining that aircraft in an airworthy condition

... but what is not made clear is whether it is an offence to operate fly your own aircraft without FAA airworthiness certification.
With regard to Hughes' home-built rocket, the FAA definition of aircraft surely qualifies this device as an aircraft, (although,  owing to its speed, not an ultralight which have their own waivers). Further, there was no intent or pretence to go to space, so the SpaceX / NASA rules don't seem to apply here.
It seems to carry no registration, nor the mandated "EXPERIMENTAL" marking one would expect if it were - however, it is noted that in the US an aircraft does not have to be registered to be certified airworthy (although they usually are).
Should this sort of aircraft fly with an airworthiness certification? And if it didn't, why not?
NOTE - this is neither the place nor the time for a discussion of the wisdom of Mr Hughes' venture.

source
.

"With regard to Hughes' home-built rocket, it surely qualifies as an aircraft"  In what sense of the word?  I know of no aircraft that takeoff vertically and land via parachute.  In my readings of the FAR/AIM (Federal Aviation Regulations / Aeronautical Information Manual) over the years, I don't ever recall seeing Rocket mentioned except as a hazard to flight.

Hi, as I say in the question, this (non-space) rocket qualifies as an aircraft because the FAA definition of an aircraft is "A device that is used or intended to be used for flight in the air". There's a separate definition for airplane, which obviously this isn't. Clarified in the question, thanks.

I think perhaps this craft would fall into this category instead  https://www.faa.gov/about/office_org/headquarters_offices/ast/licenses_permits/sub_orbital_rockets/  Experimental Permits for Reusable Suborbital Rockets.
The Commercial Space Launch Amendments Act of 2004 (CSLAA), ... directs the Secretary of Transportation and, through delegations, FAA, to establish an experimental permit regime for developmental reusable suborbital rockets. Under the CSLAA, FAA can issue experimental permits rather than licenses for the launch of and reentry of reusable suborbital rockets.

@CrossRoads it’s a nice link but inapplicable as this is a private venture carrying only one flight crew member and not for compensation or hire.  As such commercial space laws authorized by the Commerce Clause of the US Constitution would not have an effect here, though the recommendations on the FAA’s website are pretty sound.

related "in space": Is there some fundamental limitation that would prevent steam-powered rockets from reaching space? and also Latest Mad Mike Launch

"this (non-space) rocket qualifies as an aircraft because the FAA definition of an aircraft is "A device that is used or intended to be used for flight in the air" -- so is a trampoline an aircraft in the eyes of the FAA?  How about a pogo stick?   Of course most pogo sticks would qualify as ultralights, and likewise most trampolines.  How about a trebuchet weighing at least 255 pounds, employed to launch people?  How about a cannon used to fire a human cannonball?  Are those aircraft, and more specifically, non-ultralight aircraft?  Just kind of brainstorming out loud here.

Interesting topic.  Rockets and spacecraft are still highly experimental vehicles and are recognized as such under 14 CFR §1200.  The laws, liabilities, and regulations for private spaceflight are largely uncharted territory at this point, though §1266.102 requires all participants aboard the ISS and NASA launch vehicles to sign a liability waiver prior to flight.  Essentially, in the eyes of the law, you’re on your own in doing this and if your injured or killed, neither you nor your estate can hold any participants in your cosmic ordeal liable.  Given that many flat earthers view NASA as the enemy of their efforts, any laws in regards to spacecraft certification would probably be viewed in a negative light and disregarded.
Using §91.7 here is pretty nebulous as there is no definition or standard here for airworthiness of such a craft.  These guys were testing an experimental vehicle at a remote site far away from other persons or property and flying only a single flight crewmember.  There’s really no law saying you can’t take a risk like that under those conditions.

So this is the reason why a rocket is used rather than a balloon? Because it's legally easier?

@user3528438 A rocket was used because the balloon's days as a "daredevil" craft expired in the 1870s.  A Part 103 ultralight would have gotten Mad Mike to his 5000 ft AGL target, slower and safer and cheaper, and allowed staying there long enough for photographic "proof" to be obtained -- but slower and safer weren't the goals; launching himself by rocket was the goal.

I've clarified the question a bit; surely this wouldn't be considered as any sort of 'space' rocket, the intention was to go to 5000 feet, and as such seems to me governed as any other aircraft, despite its unconventional power-plant.

I’m leaving the flat earth comment in there as it is relevant to compliance by a third party in such a matter.

@CarloFelicione Was he still sponsored by the Flat Earth Society or a subgroup for this last flight?  I know the previous one was, but I understood his sponsorship had changed.

I can’t answer that but he is a well known flat earthier, similar to Mark Sergeant or Patricia Steer.


text:
How does a Hawk jet avoid pitching down when its air brake is applied
Some aircraft have air brakes in an aerodynamically neutral position with respect to rotational forces on the airframe (e.g. F-15)...

source
... more often, others have brakes that are aerodynamically neutral by being opposing (lots of examples, F-16, Space Shuttle, here's a Buccaneer)

source
... but the Hawk has an air brake that, because of its position at the tail end of the aircraft, and without any opposing force, I would have expected to generate a severe downward pitch as it is deployed, in much the same way as the elevator.

[source - Ministry of Defence]
It obviously doesn't, so the question is - why not?

While it's located closer the the center than the Hawk, the F-15 air brake will still cause some nose up force from the drag component.

It did generate a nose down pitch moment, but the tail had enough control authority to deal with it in most cases. Airbrake extension at greater than 450kt produced an unacceptable trim change.
Efforts to increase control authority to counter "phantom dive" caused by tail stall during simultaneous flap and gear extension helped. The solution was to affix a leading edge extension to the tail, but since the tail was all moving it was felt that the structure would not be able to handle the extra load. Instead, the tail LEX was affixed to the fuselage and still gave acceptable results.

A later version, the Goshawk, developed as a military trainer for the US Navy had side mounted airbrakes, though this was done to facilitate the installation of an arrestor hook. This photo shows the LEX just above the side mounted airbrakes.

Hawk mk100 with ventral fins, center airbrake and tail canard LEX.

Thank you very much, but I'm a bit confused. The diagram you posted shows these tailplane LEX canard extensions (which are present on the Goshawk but not the Hawk T1) AND it shows the smaller ventral fins (which are present only on the Hawk T1 - the Goshawk has a bigger, single ventral fin).
Either way I believe the extension you've shown isn't used on the Hawk, and I don't think its ventral fins can have much effect on pitch (are they non-moving? I think so.)

The term "tail canard" really confuses me. AFAIK a canard is always ahead of the main wing and is a moving surface. I would call the devices in front of the hor. stab. "strakes."

@TomMcW That was the term in the reference and I agree it is not ideal. I used the term LEX since it works through vortex generation and would have been integrated into the horizontal stabilizer if the structure could have supported it. Strakes unfortunately does not work in this case because there are actual ventral strakes in this application and calling both structures the same thing would be even more confusing.

@PartyArk Canard extensions were added to the Mk100, which also had the ventral strakes. If you read the explanation of canard operation in the reference, the intent was to increase control authority by generating a vortex across the horizontal stabilizer. I have added a cutaway showing all three features on the Hawk: the side ventral strakes, the center airbrake and the canards.

@Pilothead: So call the ventral ones "ventral strakes" and the lateral ones "lateral strakes".

source: Stack Exchange

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sort: votes


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How is structural damage to a composite fuselage detected?
When a service vehicle collides with the aircraft, the plastic nature could hide any subsurface fractures which could propagate as the aircraft goes through cycles.
How is potential damage diagnosed on the A350 or 787?

Related: A review of non-destructive testing methods of composite materials and The Challenges Of Detecting Composite Damage

I can't personally speak for the Airbus, or Boeing methodology regarding damage diagnosis, however speaking as an A&P IA FCC, experienced in the Business, and General Aviation Industry, the diagnosis will employ, one or a combination of all of the following inspection methods:

Visual
Coin-Tap
X-Ray
Ultrasonic

Welcome to Aviation.SE, while this is correct, it would be good to explain them a bit more and maybe provide some links to further reading.

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In the US, what can be done at an airport when volunteering hours?
I am a 15 years old and need volunteering hours for my course work. I am a aviation enthusiast with knowledge of the industry and love for anything that flies. I decided to fulfill my hours at a local airport because I would be helping others doing what I love. I am from Florida, and I know this is the greatest place for all aviation related things.
The tasks I would like to perform at my local airport are fueling, taxiing aircraft in and out of a ramp, and help with other airport operations.
Is any of this possible?
If anybody can give me any idea on how to do this. I also like any advice to help me further my volunteering path with other aviation related tasks.

Which airport? Some commercial airports have volunteers that staff information desks, help direct passengers, even to bring around dogs for passengers to pet. It's not taxiing aircraft, but it would be a way to get a foot in the door. You'd need to contact the airport's management to see if they have such a program and whether you're eligible.

Commercial airports are challenging for volunteers because of security, if you want to do anything beyond the security barrier (ie where the interesting stuff is) then you need to be cleared and supervised, and that costs time and money.
There may be opportunities at small airports, which don't have the same security concerns. Most won't have any established volunteer positions, it would be more of a case of talking to the airport manager or someone running an FBO and asking if there's anything you could volunteer for. Ask politely, wait a few days, then follow up with a phone call, if they know you're genuinely interested (and polite, sensible, not likely to run into a propeller) they might be willing to offer something to you.
One last thing, if anyone asks you to get a bucket of propwash it's an old aviation joke.

Working as a volunteer at an airport may be problematic, because almost everything at most airports is (a) a for-profit enterprise, and (b) involves liability. Those factors make it more likely to use paid, trained, accountable employees instead of volunteer temporary help.
That said, there are aviation-related volunteer opportunities out there if you can expand your criteria a bit. Aviation museums tend to do lots more with volunteers, and that would be the first place I'd suggest looking for leads. You won't be fueling or taxiing aircraft, but working around docents with a career of aviation experience, you'll pick up a wealth of stories & advice.
Some large airports may have volunteer greeter positions (i.e. "Which way to baggage claim C please") available, but I'd start with museums for a closer connection to fliers & flying machines.
Best of luck in your search!

Civil air patrol.  They fly GA aircraft in service to the nation.  Technically an auxiliary of the Air Force, they do search and rescue, disaster relief, aerospace education, a cadet program, homeland security, assisting law enforcement, all sorts of things.  And yes, they have a youth program.
Aviation museums.
And one that many people overlook, naval aviation museums.   Like the USS Intrepid, Midway, Hornet etc.

I would go to your local airport and contact the manager. Many airports have a public space, and most of the ones I've been to could definitely use some attention.  You could see if there are touch up jobs you could do there. I'm wondering if railings need new paint or new signs could be placed. Paint parking stalls. Replace tie downs. Others have mentioned liabilities working around aircraft. I don't image you could do much that involves being near or interacting with planes without waivers and training...
Also, lots of airports like to host events. I've been to many of these and there is often a lot going on. I'm sure there is a way to volunteer there, even if its just taking tickets at the gate or guiding visitors.
Good Luck

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Is there AOG liability?
From Wikipedia:

Aircraft on Ground or AOG is a term in aviation maintenance indicating
  that a problem is serious enough to prevent an aircraft from flying.
  Generally there is a rush to acquire the parts to put the aircraft
  (A/C) back into service, and prevent further delays or cancellations
  of the planned itinerary.

I know AOG is a really serious issue for an airline. What I want to learn is the liability and how far it extends. For example; if AOG happens:

how long can this airplane stay in that airport?
what is the airports role in this situation? Do they help them out or just charge the amount they stay on the ground?

@Notts90 probably I should, thanks for advice. I will edit accordingly and ask seperate questions

how long can this airplane stay in that airport?

The aircraft is "AOG" so it cannot leave. It needs to stay as long as it takes to complete the necessary repair.

what is the airports role in this situation? Do they help them out or just charge the amount they stay on the ground?

The airport usually would charge the airline the parking fee. The parking fee is a small cost of not having an aircraft available in revenue service.


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Do aircraft have radar or other forms of traffic sensing?
Quicky question.
Do modern commercial aircraft include radar to detect traffic in their vicinity or perhaps have some mechanism to receive transponder signals.
I know they have forward facing weather radar but the ability to detect and be warned of other traffic on a collision course would seem to be a good idea.
I'm particularly reminded of the Proteus Airlines Flight 706 incident where a mid-air collision occurred because of visual blind-spots and the ATC not knowing the other aircraft was even out there. I am also aware in this case a transponder monitor would not have helped either...
EDIT:
I suppose TCAS does do the transponder bit, but wont detect aircraft without the necessary device turned on. I'm more thinking of a short range RADAR or even LIDAR, something akin to, though longer range than, the things they are hooking up to cars these days.

Are you talking about something like TIS-B and TCAS? Or something else?

https://en.wikipedia.org/wiki/Traffic_collision_avoidance_system

I suppose TCAS does do the transponder bit, but wont detect aircraft without the necessary device turned on.

A part of the answer is that IFR-IFR collisions are prevented by ATC (traffic surveillance).

A radar that can see all around the aircraft (instead of just a sector in front of it) is large and complicated, see the radar installations on AEW aircraft.

By far, most civil aircraft lack radar to display conflicting traffic, and certainly to enhance traffic situational awareness.  TCAS and the use of ADS-B are the most effective tools for traffic conflict and situational awareness information.
Lidar is not presently utilized on civil aircraft for traffic avoidance.
Keep in mind that TCAS essentially uses the same mechanisms as secondary ATC radar.


text:
How do I get a Special Issuance?
On the FAA medical exam there is a conditions section and one of them is mental disorders. I have/had OCD so I have to check yes. I'm getting off my med soon and then I will have another exam, so that I don't have to check this element anymore.
I heard I could use a Special Issuance to get a medical certificate. How do I request this Special Issuance?
On the FAA website it says:

The applicant must demonstrate to the satisfaction of the Federal Air
  Surgeon that the duties authorized by the class of medical certificate
  applied for can be performed without endangering public safety for the
  validity period of the Authorization. The Federal Air Surgeon may
  authorize a special medical flight test, practical test, or medical
  evaluation for this purpose.

My OCD is not and was never that severe, I never had depressive episodes. I have a flight simulator and I don't repeat actions or have to check over and over again, or make sure everything is perfect; My OCD wasn't like that.
Right now I'm in contact with leftseat.com. They say they can get me a medical certificate, but nothing in the document they gave me mentions meeting a Federal Air Surgeon. I'm just really confused, as I think I need to meet one for the Special Issuance.
Could someone clarify this?

You don't meet with the air surgeon. They review the records, test results, etc. provided by you or your AME and make a decision on the SI

As with most specific medical questions, the only real answer here is "talk to an experienced AME, preferably one who's handled similar cases before". Some standard advice is to schedule a consultation only first, to review your case. Once you have everything organized and documented properly and your AME is confident about your application, then you can do the actual medical exam.
Having said all that, as far as I know you don't request an SI directly. If the AME determines that he can't issue a medical certificate because of a condition you have, he should work with you and the FAA to put together whatever combination of test results, documentation and general information that the FAA wants in order to issue an SI. But all of that should happen before you do the actual medical exam, to avoid delays.
If you're an AOPA member they can help you with advice and information and they have more details about the SI process. (Their medical forum is very useful too).


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How does the size of each stage vary in a high pressure compressor?
Is it true that in the high pressure compressor the stages and blades on the stages get smaller as it goes on?

Yes, the volume of the annular air channel goes decreasing after each stage. When air is compressed it takes less volume. Each stage compresses a bit more, hence the volume is constantly decreasing. This is also true for the low pressure compressor.
In this cross-section, the two spools, low pressure in red, and high pressure in green, display clearly this progression.

Turbofan compressor section (GE90), source
The first stage of the high pressure compressor is longer than the last stage of the low pressure compressor, but note the annular space of the high pressure section is smaller than the low pressure section due to the mean diameter reduction. In addition the HP spool rotates at a higher RPM.
Engine from the same family, in 3D:

Turbofan cutaway, source
The reduction of volume can be achieved by decreasing the outer radius of the air channel, by increasing its inner one, or by adjusting both. The number of blades/vanes can also be increased as pressure increases, to prevent deformation.


text:
Does SDAC display data for both the PFD, ND and the ECAM display?
On the Airbus A320 the System Data Acquisition Concentrators (SDAC) aquire system data, process it and sends system page data to the three Display Management Computers (DMC). The DMC process the data and generate an image.

Is this for the PFD and ND only? Or does the DMC also generate the image for the upper and lower ECAM too?

EIS, source
If the lower ECAM, supplied by DMC 2, fails then the E/WD displays which has priority take its place; and DMC 1 normally supplies the Engine/Warning Display (E/WD).

Does it mean DMC 1 has a channel or a way to display on the lower ECAM as it just did?
Likewise, does DMC 2, which normally supplies the lower ECAM, have a channel or some sort of way to display on the upper ECAM?

The DMC can process simultaneously 3 pages among them only one system page. DMC 1 and DMC2 are linked to both central displays.
Therefore the display page arrangement is done by the DMCs not by the SDACs, nevertheless lot of data computed by the SDACs are displayed on the ECAMS and on the PFD and on the ND:

On the ECAMs for instance all system pages and AMBER alarms via the FWCs
On the ND and on the PFD flags and degraded conditions, such as the cross « X » when data is NOT computed for the relevant parameter.

Of course my answer is not exhaustif but sufficient to justify that the SDACs are concerned by data displayed on all EIS displays.

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text:
Why are there motive flows for the turbine pumps of Williams International FJ44-3A engine?
For my university project, I am designing the fuel supply of an aircraft using a Williams International FJ44-3A engine.
Studying the related FAA TCDS, I read "Fuel from the motive flow port on the fuel control unit may be extracted to drive jet or turbine pumps in the airplane fuel system". About these pumps:

What is a turbine pump?
What is it used for in this engine?
Why would this pump be driven by the motive flow?

I did look into that question before, but it doesn't answer my question of why does the TCDS said that the motive flow is used on the turbine pump and not the primary fuel boost that answer mentioned. It also didn't answer my question of what is this turbine pump.

The exact sentence in the certificate is: "Fuel from the motive flow port on the fuel control unit may be extracted to drive jet or turbine pumps in the airplane fuel system", the linked question explained what is a jet pump. Now you would like to know what a turbine pump is, so let me edit and simplify your questions. Feel free to roll back to the previous version if you prefer your version. You may want also to update the title to reflect your current needs.

The certificate does state such motive flow is available at a port of the FCU and it can be used to drive pumps, either jet (ejector) or turbine pumps. It doesn't say these pumps are already in place, but if they are installed, and if their design matches, they can be powered by tapping the related port.
This question: What is motive flow and why is it used in some aircraft hydraulic systems? explains both the motive flow and jet pump concepts and what are the main uses of jet pumps (e.g. fuel boost and scavenge pump).
So the only missing element is what is a turbine pump. It's a pump which is driven by a turbine. A turbine in general is a device converting fluid energy into rotational motion, like in a turboengine. Here the fluid would be fuel from the motive flow. It would turn the pump. The pump itself can be used to move a fluid, likely fuel, like in the jet pump.
The choice to drive pumps by the motive flow is to rely only on the engine for providing the energy. Once started, this system engine-pump is autonomous.
This is similar to using fuel as a power source for other elements in an engine, e.g. moving variable blades.


text:
How do insurers apportion responsibility when airliners collide on runways or taxiways?
Here's an ATC recording of Virgin and Egyptair aircraft clipping wings at JFK.
Generally, what happens next with regard to sorting out responsibility after a low-speed collision that results in damage to commercially-operated aircraft? (I'm talking about a return-to-gate type of collision where passengers are inconvenienced, rather than a serious evacuation-style incident.) There seems to me lots of factors, for instance:

The captains are in charge of their aircraft, but what if ground controllers gave them poor instructions?
When a parked aircraft were damaged by a moving one, the former might seem the innocent party, but what if it were stopped in the wrong place?
It's possible that an airport itself might have listed incorrect information about its taxiways that leads to a collision.

In automobile accidents, its the insurers who would sit down and come to some agreement, but there's not really an equivalent of the airport in such circumstances. And the stakes are quite high - repairs and delays might be very costly to an airline.
I presume there's always some sort of regulatory investigation, but their prime concern I would think is to stop it happening again, which is not the same as agreeing responsibility and liability. The question is: how do insurers decide who ends up paying, for what is almost always a very expensive error?
 source

You need to narrow this down, do you mean from an insurance point of view, a regulatory investigation point of view?

Before I ask a separate question, could someone say whether a low-speed on-ground accident is investigated in the same way and by the same people as an accident in the air?

@GdD That's part of what I'm asking - does the insurance take it's lead from any regulatory investigation? Or perhaps they're entirely independent. But I'll take out the bit about the pilots, that probably a separate question.

Just a note, those two aircraft did not collide on the RUNWAY! That would have likely resulted in a very different outcome

Yes you're right, I meant the airport generally will amend my question.

Insurance is a contract between the airline and the insurance company. Typically, the airline is simply compensated an amount by the insurance company and the case is closed.
Demand to another party for settling damages only occur if the damages is unusually large and one party is mostly at fault. You have to consider the time and cost taken into legal proceedings as well.
Insurance compensation actually occur more frequently than you think. For example, at my airline, someone either forgot to apply the brakes on the food trolley or the brakes failed. Either way the trolley smashed into something during ground operations, resulting in damage to the trolley itself (I heard it was destroyed). Insurance paid us.
Regarding the specific incident about airplane collisions on taxiways, it is highly unusual. My guess would be it was handled as a "special case" in this instance.
You are correct that any investigations, if any, focus on preventing future occurrences rather than assigning blame. Settling damages is a civil matter; as such insurance companies rarely launch their own "investigations". Even if they do, it would just be a corporate and expensive version of two drivers using dash cams to argue who has to pay for the stretched bumper.
At any rate, insurance may compensate the airline even if employees of the airline are at fault. That is what insurance is for.


text:
What factors govern the placement of a helicopter's tail rotor (left or right)?
An image search for 'helicopter' indicates that there isn't a consensus on whether to place the tail rotor to the left or the right of the tail boom, although I'm believe there may be a bias for left.
There never seems to have been a consensus: taking two popular early helicopter designs, the Bell 47 has its rotor on the right; the Hughes 269 on the left.

Bell 47 source

Hughes 269 source
There are many left/right conventions in aviation, e.g. where the pilot sits, which side the passengers exit etc. So the question is, what governs the choice, and would it be beneficial if a 'right' side was generally agreed on?

Perhaps you'd also be surprised that there is no consensus regarding the rotation direction of the main rotor. Generally speaking, western helicopters' rotor will spin counterclockwise (except for helicopters built by Aérospatiale), while eastern  will spin clockwise

Which may go part way to explaining rotor position: assuming tail rotors always pull rather than push (that's a guess), then it's the main rotor's spin direction which would dictate left or right for the tail. (However, there are lots of examples of both left and right western helicopters from many different manufacturers.)

Not necessarily. The tail rotor on the Blackhawk is on the right

note also that the rotors of the two copters in the question spin in the same direction.

ok, interesting, so if the main rotors spin in the same direction, presumably one of the tail rotors pushes and one pulls?

@DeepSpace East versus west? Surely they spin one way in the northern hemisphere and the opposite way in the south! ;-)

It's hard to say the design rationale used for all helicopter manufacturers. Push vs pull doesn't seem to be very important.
One example is the Bell UH-1 Huey (Left side Pull). When Bell modified the design for civilian use 205, 212, 412, 214, they put the TR on the (RH side Push). When asked about the reasoning for the original Huey/205 change, Bell engineers explained that they found better TR effectiveness with rotation of forward blade climbing, as the interaction with wake and vortices of the main rotor was more favorable in this configuration.
Now look at the AH-1 Cobra Gunship variants. Bell switched sides at least twice. Left on early models, switched to right on later 2 blade models (AH-1W). Back to Left side for the 4 blade AH-1Z. While on opposite sides, the AH-1W and AH-1Z are both forward blade climbing.
Sikorsky? S-76(Left - Climbing) H-60(Right - Climbing) H-53(Left - Climbing). One could speculate that the higher the TR is mounted, the more this rational comes into play.

Location of the tail rotor is the result of mainly:

Tractor or pusher type: blow against the vertical fin or away from it. If against the vertical fin, there is a beneficial pseudo ground effect on the tail rotor. The pusher type has the vertical fin slowing down the inflow, which produces a pseudo ceiling influence which is beneficial as well
Rotation direction of the main rotor.

Ray Prouty (In Helicopter Performance, Stability and Control) has this to say about pusher/puller:

The tail rotor can be installed either as a pusher or as a tractor.Test results...show that the pusher is more efficient since it is less interfered with  by the vertical fin. Nevertheless, there may be reasons for using the tractor installation. For example, on the Sikorsky UH-60, the designers decided to tilt the tail rotor shaft to take advantage of a vertical component of tail rotor thrust. To obtain adequate clearances as a pusher, the tail rotor shaft would have had to be very long. As a tractor, the installation was much lighter and compact.

Data on the effects of pusher/puller can be found in Leishman (Principles of Helicopter Aerodynamics), showing that the interference effect is most beneficial if the obstruction is not in the high energy flow. It also shows that with USA helicopters, the pusher is on the left side and the tractor on the right. For European helicopters this is the other way around since the main rotor turns the other way.
The two helicopters in the OP have no vertical fin, and then the decision is basically arbitrary.


text:
Why do navaids noted in the chart supplement have a W next to them?

Why do navaids noted in the chart supplement have a W next to them?
Thanks

“Most VORs are equipped for voice transmission on the VOR frequency. VORs without voice capability are indicated by the letter “W” (without voice) included in the class designator (VORW).”
I assume the same thing applies to VORTACs.
Source: AIM Navigation Aids 1.1-3 VHF Omni-directional Range (VOR)
https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap1_section_1.html

It applies the same to VORTAC, the VOR portion has no voice channel, the DME portion is not concerned.


text:
Why does forward CG decrease controllability/maneuvarability?
Why is a larger elevator input required to change the pitch of an aircraft with a more forward CG? I would think intuitively that the farther forward the CG, the greater the arm between the elevator and the CG, and therefore the greater the moment.
Thank you

Intuitively:  the farther forward from the center of lift that the CG is, the greater the "lever arm" that inertia has in keeping the airplane doing what it's trimmed for.  That effect overwhelms the slight increase in distance from CG to elevator.  For a typical small airplane, moving the CG forwards by a foot might double the lever arm of inertia, but increase by only a few per cent the lever arm of the elevator.


text:
Can you be paid to be a safety pilot?
If you have a commercial certificate, can you be paid to be a safety pilot for someone else shooting approaches under foggles?
Thanks

Yes, as a commercial pilot with a valid Commercial Pilot License (CPL), you are permitted to be remunerated for acting as a safety pilot.
In the scenario described, I am assuming it involves a single-pilot operation, meaning it does not require a multi-crew aircraft. In this case, you would be the Pilot-in-Command (PIC). The individual performing approaches could be considered the Pilot-in-Command Under Supervision (PICUS), but you retain ultimate responsibility as the PIC.
According to regulations:

c) to act as pilot-in-command, in commercial air transportation, of an
aircraft within the appropriate category and certificated for
single-pilot operation.
(ICAO Annex 1 - 2.4.2 CPL Privileges)

Though a training flight would not strictly fall under being "commercial air transportation" by ICAO definition, the same regulation would probably apply within your NAA for being allowed to receive remuneration for such a training flight as still being a "commercial operation" (see FAA Part 91, 121, 135 / EASA Part-SPO). This is ultimately "tidied-up" if you are operating within an Approved Training Organisation (ATO).

If the operation involves an aircraft certificated for operation by more than one pilot (multi crew operations), you could still be remunerated. However you would have to be a safety pilot on the jump seat, as an Airline Transport Pilot License (ATPL) holder would need to serve as the PIC (ICAO Annex 1 - 2.4.2). You can't be PIC of a multi-crew operation with just a CPL.
Example of this type of flying would be during "base training" - flying the visual circuit with no passengers, or being a jumpsuit safety pilot on the first few sectors of airline experience before being "safety pilot released."


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Is it legal to hold out if you DO NOT have operational control?
Let's say Bob just got his commercial certificate. He decides to have leaflets printed up advertising his willingness to fly other peoples' planes for hire. Bob then goes around to local airports handing out these leaflets. Clearly Bob is holding out. But in the case of these potential revenue generating flights, he does not have operational control over the planes and/or flights. Is Bob breaking the law? Also, would these flights fall under common carriage?
Thanks

Substitute the word "resume" for "leaflets".  Does that alter your perspective on the question?  (Hint:  it's perfectly legal to look for a job, it's not legal to start an air charter service without a part 135 operating certificate.)

Yes, this is legal.
Just the act of "holding out" is not against the rules. "Hold out" is a transitive verb; it requires some object, some thing/idea which is being held out.
AC 120-12A lays out what defines a common carrier:

(1) a holding out of a willingness to (2) transport persons or property (3) from place to place (4) for compensation.

Providing transportation as a single package, in exchange for compensation, is the defining characteristic of a common carrier. "I will be flying this aircraft from San Jose to Los Angeles at 10:00 on Sunday morning. Anybody who likes may come with me, if they give me $100." That is what an air carrier does.
If Bob is advertising his services as a pilot and no more, that is not common carriage. "I am a licensed commercial pilot and if you point me toward your aircraft and tell me to fly it to Los Angeles or anywhere else, I will fly it."
Now Bob does have to be careful that he is not accidentally joining in someone else's illegal common carriage scheme, a so-called "134.5" operation in which Bob's employer is selling tickets on a flight—just as an air carrier would—without having the proper air carrier certificate. Even if Bob is simply providing his pilot services to an employer, it would still be his PIC responsibility not to break the law by flying for a 134.5 operation. But if Bob's employer hires Bob to fly their family to their vacation down in Los Angeles that is private carriage.


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Density Altitude and Cruise Performance
Obviously higher temperature than standard and lower pressure than standard (high density altitude) hurt takeoff performance. The wings have less air molecules to produce lift with, and a typical piston engine will produce less power. But does this translate to less range/fuel endurance in cruise? The performance charts of the PA-28 I fly seem to indicate the opposite.

As you go to higher altitude and the density drops, you end up flying at higher true airspeed to compensate.  Namely, you want to fly at about the same lift coefficient (and thereby the same L/D) independent of altitude.  Since your weight is the same, and $C_L=W/(q S)$, you hold constant dynamic pressure (q).
$q=0.5\rho V^2$  Flying constant dynamic pressure works out to the exact same thing as flying at constant equivalent airspeed -- KEAS.
However, holding constant KEAS with increasing altitude means you're flying at higher KTAS.
The power required for flight will increase -- $P=D V$.  The drag will be constant, but the velocity (here true) is increasing.  Depending on whether you have a fixed pitch or constant speed prop and where you are in its operation, your propeller efficiency might increase or decrease a bit.  Your BSFC might also increase or decrease slightly depending on details of the required throttle setting.
The 'getting there faster' and the 'burning more fuel per hour' cancel out and you end up with pretty much constant specific range (miles per gallon) for a piston prop aircraft (when varying altitude).
However, humans value getting someplace faster, so it is preferred to fly higher.  In fact, aircraft are often operated at slightly faster than the speed for best range -- the extra fuel required is small, but it can come with meaningful time savings.

Both higher temperature and lower pressure mean lower air density. This will allow the plane to fly faster at the same polar point. The higher temperature will hurt engine efficiency a bit, but the effect on flight speed will outweigh this, so a net gain in true air speed versus fuel flow could remain, depending on propeller characteristics.
Reasoning: To fly at the same polar point, dynamic pressure must be the same. Lower density needs higher speed to keep dynamic pressure constant, so true air speed goes up with the reduction of the square root of density.
The efficiency of heat machines is proportional to the ratio between the temperature difference within the cycle divided by the maximum absolute temparature. However, given the wide spread between air temperature and the highest temperature during combustion, the change in true air speed is larger, so the reduction in efficiency will be smaller than the gain in true air speed. Since your measure of performance is range in cruise (ground covered for fuel burnt), a higher true air speed at the same fuel burn will directly increase range.
Details now depend on your propeller efficiency over true air speed: For a fixed pitch prop it could go up or down, depending on where the speed for best prop efficiency is relative to flight speed. For a constant speed prop efficiency drops, basically eating up the gain in fuel flow over speed.


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Is there a way to tell if a navaid in the plan view of an approach plate is collocated with DME equipment?
If there are DME distances depicted in the plan or profile view of an approach plate, it is usually pretty obvious which navaid they are referenced to. I'm wondering if there is a way to tell definitively if a navaid has DME by some indication within the navaid box depicted in the plan view.
Thank you

Can you provide an example? What chart provider are you referring to? Otherwise, the symbol used should indicate if it is a VOR/DME, TACAN, VORTAC, or DME-only facility.

Do you have an example of a navaid depicted on a chart where that information isn't available either on the chart legend or on the depiction itself (i.e. a "DME" notation or a TACAN channel such as "ch 112")? Between those two references, I can't think of a time that DME availability isn't clear, but do you have an example where it isn't?

As best I can tell from inspecting a few plates, approaches use the same symbology as vfr / ifr charts. So a VOR is a hexagon, a VOR/DME is a hexagon inside a rectangle, a TACAN is a kind of 3-lobed thingy.


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Half-Standard Rate Turns and Turn Coordinator
What does a half-standard rate turn look like on a typical turn coordinator? Is the wing tip exactly between the "wings level" mark and the standard rate mark? I am not asking about turn-and-slip indicators, just turn coordinators.
Thank you

Interesting question actually. I couldn't find any info on whether the gyro's displacement is linear or not when it's canted 30 degrees.  I assume so, and imagine banking to the middle of the range gives you a 1.5 deg/sec turn rate, more or less.  Ballpark is all you need, since precision isn't possible anyway.

If you are asked to do a half-standard rate turn by ATC, then you should indeed do a turn where the wing tip is halfway between the wings level marking and the standard rate marking, unless your turn coordinator has a specific mark for half-standard rate turns.
This will probably not be exactly half a standard rate turn. Turn coordinators are calibrated to show a standard rate turn during a coordinated level turn of standard rate at a specific true airspeed. There is no such calibration requirement for half-standard rate turns, and even if there were it would only be exactly correct at one specific true airspeed.
But this really doesn't matter. If you're asked to do a half-standard rate turn, ATC really isn't expecting you to successfully do exactly 360 degrees of turn in 240 seconds. If you're doing timed turns they don't expect you to roll out on the exact heading they would like. That level of precision simply isn't possible or expected.

You can experimentally test it on your own equipment using the formula:

rate of turn is proportional to tan bank angle/Velocity

and see how your turn indicator displays
Most applications for turn indicators are to "do a 180" course reversal to get out of a bad (weather) situation.
But if you wish to try 1/2 standard rate, use the attitude indicator to set the proper bank angle for your speed based on the bank angle for a standard rate turn at the same velocity.
With the tangent function, the comparison of bank angle to tangent angle is not quite linear, but close:
10 degrees.        0.176
15 degrees.   0.268
20 degrees.   0.364
30 degrees.   0.577
40 degrees.   0.839
The bank angle for a "1/2 rate turn" will be approximately 1/2 that of a standard rate turn.  Velocity can also be adjusted a bit if you want to "fine tune" it.


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Do airliners have any cockpit indication of open doors?
A recent report into an "unnecessary" plane evacuation reports that, following an aborted takeoff

[The senior flight attendant] then ordered an evacuation of the 169
passengers onboard, but the pilot and co-pilot were not informed nor
aware until they noticed the evacuation slide had been deployed and
passengers were moving across the front of the aircraft. [my emphasis]

This led to dangerous situation because the pilots, unaware of the evacuation, kept the engines running while the passengers were trying to get out.
It raises questions about crew and cabin crew communication, but what I found most surprising is that apparently there is nothing in the cockpit to alert the pilots that the doors had been opened.
Even my car does that!
Is this something specific to the A320 or is it generally true that the cockpit doesn't 'know' what's happening with the doors?
 Laudamotion Airbus A320-214 which had emergency evacuation (source)

Your quote "until they noticed the evacuation slide had been deployed" sounds like the ECAM indication.  The FA initiated the evacuation without communicating with the pilots, and they became aware because of the ECAM, followed by seeing passengers on the tarmac. Is that a reasonable way to read what you quoted? "Noticing" the slide deployed well behind you by craning your neck to look that far over your shoulder seems like a less likely first indication, especially with "stuff" going on in the cockpit.

Your comment prompted me to look at the actual AAIB report -
"At 2007:21 hrs, just as the commander was about to make a PA to instruct the FA to return to normal operations, he noticed an amber ‘DOOR L [LEFT] FWD [FORWARD] CABIN’ caution message illuminated on the ECAM. At first, he thought it was a fault but then saw the evacuation slide deployed at Door L1 out the left cockpit window and passengers moving across the front of the aircraft." - so, it was actually seeing the passengers that caused the pilots to realise what was actually going on. But it answers my question about the cockpit.

The Airbus A320 has an ECAM (Electronic Centralized Aircraft Monitor) Door Page:

(A320 FCOM - Doors - Controls and Indicators)
When a door is opened, this will also trigger a caution. According to the FCOM, a MASTER CAUT is triggered together with a SINGLE CHIME. The lower ECAM page will also automatically switch to the Door page.
Other aircraft may have similar pages or individual warning lights, like e.g. the Boeing 737 on the overhead panel:

(Boeing 737 NG FCOMv2 - 1.30.15 - Airplane General, Doors - Controls and Indicators)

I can only speculate why the pilots did not recognize the open door earlier in the incident you linked. My best guess would be that they were preoccupied with the engine failure that had just occurred, which will obviously create a lot of other warnings. It is easy to miss the door warning in all of those.

I remember reading about QF32 and was quite surprised that it took the FO half an hour to go through all the ECAM alarms, warnings, messages, etc. I imagine, an "open door" message might easily get lost, even though in this case the list of messages was probably not quite that long.


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Trailing edge flaps use
Why is it that trailing edge flaps are only used at lower speeds?
Can they be used at higher speeds too?

Normally flaps are only used to increase drag and lift for low speed operation. There is no benefit to extending them at higher speeds, where they just reduce efficiency, and they generally aren't designed structurally for high speed operation, with a few exceptions.
Some fighters in WW2 had a "maneuvering flap" setting that could be deployed at speed temporarily to allow tighter turns. The P-38 Lightning had this feature, operated by a switch on the control column.
In rare cases a pilot may want to extend flaps slightly to effectively change the wing incidence to reduce the deck angle in cruise. You could do this with the DeHavilland Beaver. If you wanted to, you could cruise with the flaps extended about 5 degrees, when flying with heavy loads, to reduce the nose attitude. If you're in a Beaver on floats that is near max gross weight, the drag penalty from a few degrees of flap (which includes aileron droop) is not that great. Not a common practice though.

Hi, how do flaps reduce efficiency at higher speeds though please?

They increase lift by increasing camber, but the camber increase raises drag more than than the increase in lift, reducing the maximum ratio of lift to drag.  It also shifts the center of pressure aft so that trim drag is higher.  Lots of gliders have flaps that can be lowered a lot for landing, a little bit for thermalling near stall, and reflexed UP slightly for high speed dashes. The reflex up reduces camber and moves the CP forward, having an effect a bit like reducing the chord increasing L/D. You rarely see reflex used on power planes.

Hi, but how does camber increase lift and drag? I get that it increases drag ( as it’s like putting more area in front of the flow) but I don’t see how it raises lift?

@JohnM: because of that.

Lowering the flaps puts stress on the flaps and their attachments to the wings, and also increases the loading on the wing. Extending flaps at too high an airspeed can damage the flaps, their attachments, or the wings.
Beyond a certain airspeed, the stress can even cause the flaps to separate from the wing. Naturally, this will make it much harder to control the airplane and should be avoided.


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MAP in profile view of approach plate
I understand that the start of the dotted arrow on the profile view of an approach plate shows the MAP for the precision approach on a plate if the plate combines more than 1 (for example, a plate depicting an ILS or LOC approach). Even though an LPV approach is not technically a precision approach, the beginning of the dotted arrow would indicate the MAP for an LPV as well. Can someone cite me a reference document (the AIM, Instrument Flying Handbook, Terminal Procedures Supplemental, ect..) to verify this? I have been looking and I can't seem to find one.
Thank you

Which jurisdiction are you talking about?

The short answer is IAC 4, section 3.4.5.6.
The longer answer is twofold. First, an LPV approach is considered “non-precision” because it doesn’t meet the ICAO definition of precision. However, for the purposes of charting, precision and non-precision refer to whether a procedure has vertical guidance (and a Decision Altitude vs a Minimum Descent Altitude). Additionally, IAC 4 sections 3.4.5.9 and 3.4.5.11 include RNAV as a type of precision approach. An approach with LPV minima is considered precision.
Second, the Interagency Air Committee is responsible for developing the charting standards for the US government. In the specifications related to instrument approach procedures, the following is what answers your question:
“3.4.5.6 Procedure Track
A profile view of the procedure track shall be shown using an 8 weight (.020") line. The approach track shall begin toward the top of the primary facility line, unless otherwise dictated by the procedure, and shall descend to .10" above the underline, where the final approach ends and the missed approach begins.
On non-precision only approach procedures, the approach track will begin at the point specified on the procedure source document and descend to the MDA or VDP, thence horizontally to the missed approach point. The segment shall typically be 0.2" in length but length may vary due to the layout of the profile components.”
With that in mind, consider how that is aligned with the legend.


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Static port and drain hole blocked with pitot tube unobstructed
In this situation, would pitot-static instrumentation behave as if only the static port was blocked? What about if only the drain hole becomes blocked?
Thank you

A blocked static port will make the altimeter and vertical speed indicator inoperative. The airspeed indicator will function correctly at the altitude at which it first became blocked, but it will read high at lower altitudes and low at higher altitudes, since it's comparing the ram pressure to the wrong static pressure.
Because dynamic pressure is small compared to static pressure, this is likely to make the airspeed indicator essentially unusable if the altitude is changed too much. You can restore operation of all three instruments by using an alternate static port. If you have steam gauges, it is also possible to restore the altimeter and ASI by breaking the glass on the VSI.
If you can not unblock the static port, it is prudent to consider the airspeed indicator inoperative and cover it if possible. If you are on a stabilized approach with a blocked static port, the indicated airspeed will increase as you descend into denser air. The natural response to this will destabilize your approach and is asking for a stall.
The drain hole is meant to allow anything stuck in the pitot tube to escape. A blocked drain hole has no significant effect at first. Perhaps a small increase in indicated airspeed since a drain hole would tend to decrease ram pressure slightly. But if moisture and debris is allowed to build up it will eventually render the airspeed indicator unreliable or inoperative.


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Will accidentally using 1 quart of non-mineral oil during engine break in cause engine damage or lead to increased wear in the future?
One of the aircraft I rent is a Piper Warrior (PA-28) with a Lycoming O-320-D2A. I accidentally put regular oil in it today rather than mineral oil. The engine had run 20 or so hours since its overhaul when I made this mistake. From my research on this model engine, you are supposed to use mineral oil for the first 5o hours.

I wouldn't worry about it.
The use of mineral oil is mostly about breaking in the piston ring/cylinder bore interface, where the rings wear down the sharp edges of the honed bore surface, at the microscopic level, to create the ideal surface with grooves that retain oil while having flattened tops to make a smooth surface for the ring to slide over. The cylinder bore wears faster using an oil without all the ashless dispersant and anti-wear additives.
The engine will have high oil consumption until the rings have worn the bore surface the desired amount, and a drop in oil consumption to normal levels is the main sign that break-in is done. On O-320s, around a quart in 10-15 hours is typical for a broken in engine.
By 20 hours, much of the break-in process is complete and while I wouldn't switch completely to AD oil, and adding one quart of AD oil, say one 7th of the total of the mineral in the sump, might delay completion of the break-in some measurable amount in a controlled experiment, but nobody in the practical world is going to notice any difference.


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Can you lose your pilot's certificate if you are convicted of a non-violent misdemeanor that doesn't involve drugs or alcohol?
Can you lose your certificate, or be denied additional ratings, if you are convicted of a non-violent misdemeanor that doesn't involve drugs or alcohol?

Depends. What misdemeanor?

There is no specific provision for the FAA to revoke your certificate or deny you any further ones even for a non-violent felony, much less a misdemeanor, as long as it doesn't involve drugs or alcohol.
However, 61.153(c) requires a candidate for an ATP certificate to be of "good moral character." It doesn't define this. Certainly not all misdemeanors are disqualifying, but certain combinations of misdemeanors are.


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Difference between load factor imposed in a turn vs with wings level

How does the load factor/resultant load in this picture change if instead the pilot is in wings level flight, and yanks back on the yoke enough to produce 1.73Gs of centripetal/centrifugal force? In other words, is the resultant load any different if those 1.73Gs are now acting in the same direction as gravity?

The centrifugal force is the reaction to the centripetal force created by the curved motion. The load factor is the magnitude of the vector sum of centrifugal acceleration and gravity acceleration.
Gravity can be considered constant, centrifugal acceleration is not: Its magnitude varies with the radius of the curve and its direction is normal to the curve.
If you pull-up and fly a circular loop, the centrifugal acceleration is constant in magnitude, but variable in direction. It means the vector sum is not constant. Assuming a centrifugal acceleration of 1.73g:

At the bottom of the circular flight path, both accelerations are colinear, the magnitude of the sum is the sum of the magnitudes: 1+1.73 = 2.73g
At the top, accelerations are also colinear, but now they are in opposite directions, the magnitude of the sum is 1-1.73 = -0.73g
At 90° on each side, accelerations are orthogonal, the situation is the same than in the figure of your question. the magnitude of the sum is 2g.
At other locations the load factor varies with the sine of the angle between the two accelerations.

To fly a loop with a constant load factor, the effect of centrifugal acceleration must be reduced at the bottom of the loop, and increased at the top. The path would be something like:

See also:

What is the definition of load factor and how do you apply it?
Load factor and how does velocity affect it?

Thank you for the answer. Here's a tangent question maybe you could answer. Would the amount of stick force required to pull 1.73 Gs of centrifugal force (2 Gs total load) just as in my picture, be equivalent to the same amount of stick force required to pull 1.73 Gs of centriptal force by yanking back in straight-and-level flight (2.73 Gs. total load) if the airspeeds are exactly the same. What i'm getting at is this: is it actually easier to exceed the limit load factor by yanking back in level flight than it is doing so in a turn? Thanks

It is easier to exceed the max load factor pulling up at high speed (e.g. at the bottom of a curve, in French this is called a "ressource", maybe "recovery" in English, but I'm not sure) than during a turn. The acceleration can be higher and both vectors are in the same direction. You can post another question, I'm sure someone will provide more details.


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Critical angle of attack at high altitude
I remember hearing somewhere that at very high altitudes, the critical angle of attack for a given airfoil can decrease a bit. Is there any credence to this idea?
Thank you

Good reference here two answers down.  Mach number (true airspeed) appears to effect airflow over the upper wing, hence a change in critical AoA with altitude (even though IAS is the same).


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Victor airways that have a floor above 1200 ft AGL
Chapter 5, section 3 of the AIM says that victor airways are "designated from 1200 ft above the surface (*or in some instances higher) up to but not including 18,000 ft MSL."
What are the instances of victor airways having a floor higher than 1200 ft AGL? Is it just when class G airspace extends higher than 1200 ft AGL?
Thank you

Victor airway’s bottoms are higher than 1,200ft when there is class G airspace that prevents the class E from existing there.

Is there a missing "only" in this sentence, or are you merely confirming the information in the question?

I was more directly answering the question. There may be other situations but I am not knowledgeable on that.


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Minimum sink speed and maximum endurance speed
For a given airplane, are the minimum sink speed and maximum endurance speed the same?
Thankyou

It depends on the characteristics of the engine.
Minimum sink speed is the speed for minimum power required.  If your fuel consumption is generally proportional to power, then yes it should be very close to the maximum endurance speed.  We call these 'power producing engines'.
However, if your fuel consumption is generally proportional to thrust, then no, your maximum endurance speed will be at best L/D - the minimum drag speed.  We call these 'thrust producing' engines.
Both of these are idealizations and a detailed analysis will be slightly different.
In general, piston-propeller and electric-propeller aircraft are 'power producing' and jet aircraft are 'thrust producing'.  Turboprop are often treated as power producing, but it gets messy.

Minimum sink speed applies to gliding.  It is based on the aerodynamic characteristics of the aircraft.  Minimum sink speed is generally less than Vbg.  The glider is not gaining distance as efficiently as Vbg but has a lower sink rate because of lower airspeed.  V min sink is therefor useful in thermals, where the velocity of the updraft minus sink rate yields an altitude gain.

the glide slope at V min sink is steeper than at Vbg.  This means the glider is in a higher drag configuration.

Mathematically, V min sink is calculated as sine angle of descent × airspeed
Notice how soaring birds have broad heavily cambered wings with multiple tip slats.  These are not long distance gliders with streamlined high aspect wings like albatross.

the albatross will have a lower angle of descent but a higher airspeed, resulting in a greater rate of descent.

V max endurance will depend on what type of engine is on the aircraft.  A jet will have its max endurance close to V best glide, which, not coincidentally, will also be the Vx of the aircraft.  Graphically, this is where greatest excess thrust is found.
Propeller driven aircraft will have a slower V max endurance (also known as V min power) than V min sink because the prop affects the (aerodynamic) wind flow around the aircraft and the prop is more efficient at lower airspeeds.  Even though drag may be slightly greater at the lower airspeed, less fuel is used (per unit of time) due to these greater efficiencies.  No surprise that Vx is less than Vbg for prop driven aircraft.
It's important to understand that this is the source of differences between jet vs prop (or turboprop) V speeds, not because jets make thrust and props make power!  All propulsion systems (that are any good) make thrust.


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Can a CFI give someone he's never flown with a cross-country endorsement?
61.93(c)(1) says that, for each cross country flight, "a student pilot must have a solo cross-country endorsement from the authorized instructor who conducted the training..."
In (c)(2,3), the reg says that a student pilot must have a solo cross-country endorsement "from an authorized instructor" who reviews the student's flight planning.
Looking at 61-65J, my first impression is that the baseline general cross-country endorsement has to be from the specific instructor with whom the student did the cross-country training, but specific cross-country flights from A to B can be endorsed by an instructor who simply reviews the student's planning.
Thanks

I would have hoped a CFI would chime in here, but your interpretation seems correct to me.


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What is the specific regulation that requires the AFM and weight and balance information to be onboard the aircraft?
14 cfr 91.9 does require that "there is available in the aircraft a current, approved Airplane or Rotorcraft Flight Manual", but only for U.S registered civil aircraft "for which an AFM is required by 14 CFR 21.5" Reading through 21.5, it seems to only apply to a fraction of registered civil aircraft.
I've also tried looking in 14 cfr part 23 and 25, to no avail.
Thank you

Seems answered in: Which regulations require the ARROW documents?

that answer references 91.9, which doesn't seem to apply to most registered civil aircraft

But doesn't part 91 apply to all aircraft as general rules which can be made more stringent under other specific parts?

Read the full 91.9... for some aircraft it requires one thing (AFM), while for others it requires something else.


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Effect on Thrust and Power Required Curves of Flaps
I know for a fact that the extension of flaps shifts the thrust required/total drag curve higher. How do I prove mathematically that it also shifts to the left (LDmax with flaps extended occurs at a lower airspeed)? I've played around with the math of the induced and parasite drag curves trying to find an expression for where they intersect, and how flaps would change this expression. I've also looked at finding the bottom of the total drag curve (where the rate of change becomes zero),and looking at how that changes with flaps.
Thank you

You may need a POH-data calibrated power curve to see how thrust changes with flaps.

There are a few ways to go about this.
Starting from a simple parabolic drag polar $C_D=C_{D,0}+K\, {C_L}^2$, you can find that best $L/D$ occurs at ${C_L}^*=\sqrt{C_{D,0} / K}$
If you assume that deploying flaps only increases the parasite drag (increases  $C_{D,0}$), then it is clear to see that deploying flaps will increase the lift coefficient for best $L/D$.  Increased ${C_L}^*$ means you must fly slower to achieve that speed (all else being equal -- Weight, reference wing area, density).
However, if you have partial span flaps, you can reasonably assume that they will not only degrade the parasite drag (increases  $C_{D,0}$), but they will also degrade the quality of the lift distribution and thereby increase induced drag (increase $K$).  In this case, whether the speed for best $L/D$ shifts left or right depends on which has a greater change -- parasite drag, or induced drag.

Yes, this is good. Only thing I'd add/modify is V for L/Dmax is proportional to the fourth root of (K/Cdo). So, depends on whether K or Cdo has a greater percentage change.

Flaps both increase CD0, and shift the CL at which CD0 occurs.
If you have access to ESDU, paper 08013 goes through this for 2d, which is also reasonable for rough work in 3d. They also provide all kinds of equations to analytically estimate the actual change in 3d, but it's not as straightforward.
In general, CD,0 shifts in CL by half the amount the liftcurve shifts by, but the change in CD,0 itself is less straightforward.

A 2D approach to this will not capture how the induced drag is affected.  It is equivalent to saying that only CD0 changes -- not K (or a parabolic polar).


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Why the doppler effect created by the aircraft does not interest us in the conventional VOR ? And what happens to the doppler of the plane?
The doppler effect exists regardless of whether we have a conventional or doppler VOR but why are we not interested in the doppler effect of the aircraft?

Short answer
The Doppler effect is an apparent change in a signal frequency. When the source is moving relatively to the observer the distance between the source and the observer changes, thus the signal reaches the observer with a phase constantly changing. For the observer, this change is undistinguishable from a frequency change.
The apparent frequency shift value is given by $fv/c$, where $f$ is the signal frequency and $v$ the relative velocity. VOR have a carrier frequency around 110 MHz. For an aircraft approaching a VOR at a groundspeed of 500 kt, this gives a significant shift of 100 Hz. For a Doppler VOR this effect increases or decreases the station own Doppler shift by 20%.
A VOR station provides eventually two pieces of information to the receiver under the form of two 30 Hz sinusoids: Reference and variable signals. The variable signal sinusoid appears phase-shifted relatively to the reference according to the receiver bearing. At a given position and time, if the receiver gets phase values of 150° for the reference and 30° for the variable signal, then it's current bearing from the VOR is 150-30=120°. This is true both for conventional and Doppler VOR.
Thus your question boils down to whether the aircraft-induced Doppler shift affects the phase of the reference and the phase of the variable signal equally , or differently. The answer is the effect is the same on both signals, thus the difference is unaffected, for the conventional VOR as well as for the Doppler VOR.

Variable signal construction
From the two sinusoids used by the receiver, the reference is sent by the VOR station, the variable signal is the result of a collaborative work between the VOR station and the receiver. The receiver is the same for all VOR, the way the variable signal is constructed varies between the conventional VOR (CVOR) and the Doppler VOR (DVOR). Thus the aircraft-induced Doppler shift doesn't affect the variable signal the same way in both families.
CVOR
In the CVOR, the station radiates two high frequency signals: The carrier modulated by a 30 Hz reference sinusoidal signal using an omnidirectional pattern, and the same unmodulated carrier using a directional pattern. The receiver perceives this directed unmodulated signal with a variable strength, its amplitude varying according to a sinusoid at the rate of rotation of the pattern, also 30 Hz.
From the receiver standpoint, it takes the time of a full round (clockwise) for the phase of this variable signal to varies from 0° to 360°. When the beam is pointing in the direction of the receiver, the receiver sees this phase as 90°, because from a strength standpoint the curve is reaching the top of the ascending portion of the sinusoid.
The phase of the reference varies at the same rate and is synchronized so that its value is 90° when the rotating beam faces north. Thus if the receiver is on a north bearing, the difference is always 0°, if the receiver is on an east bearing, the difference is always 90°, etc.
The Doppler shift from aircraft motion affects omnidirectional and directional high-frequency signals the same way, introducing the same phase change in the two low frequency signals, thus this has no effect on bearing calculation.
DVOR principle
In the DVOR, the station radiates three high frequency signals: The carrier modulated by the reference from a fixed antenna and according to an omnidirectional pattern, and two sidebands, representing the variable signal, using two moving antennas and according to an omnidirectional pattern too. This design is a bit more complex and cumbersome.
Tens of antennas are set along a circle with a diameter of 14 m. Antennas are selected two at a time, at opposite locations on the circle, and all pairs are used successively within 1/30 s. Thus in one second, the active pair of antennas has covered 30 rounds, like the directional pattern of the CVOR. The DVOR has no directionality, so rotating the active antennas is not to radiate in some privileged direction, but to give the signal source an apparent linear velocity of 1300 m/s.
Each antenna of the active pair radiates a different unmodulated frequency, one radiates the lower sideband, the other the upper sideband. Sidebands are normal by-products of amplitude modulation, but in this case fake sidebands are deliberately created ex-nihilo in order to simulate AM. For the receiver, fixed sidebands belong to a carrier modulated in amplitude by a constant signal which frequency is the frequency difference with the carrier.
In this case the DVOR transmits sidebands at a distance of 9.96 kHz of the carrier. This frequency corresponds to the subcarrier used in the CVOR (to transmit the reference). Scanning the array at 1300 m/s creates a Doppler effect which actually changes the apparent frequency of the sidebands, by 480 Hz for a sideband frequency of 110 MHz, adding 480 Hz to the frequency of the advancing antenna, subtracting 480 Hz for the retreating antenna. This shift varies with the direction of the antenna motion, maximum when the receiver is at right angle of the antenna pair baseline, null when aligned with the baseline. Thus both fake sidebands move either closer or away from the carrier frequency at the rate of 30 Hz created by scanning the array. For the receiver this motion of the sidebands is a 30 Hz signal modulating the 9.96 kHz subcarrier in FM (the 30 Hz signal modulates the 9.96 kHz subcarrier in FM, and the subcarrier modulates the 110 MHz carrier in AM). As the phase of the signal depends on the bearing of the receiver, this signal can be compared with the reference. The DVOR station takes care of synchronizing the circular scanning and the reference phase.
The 9.96 kHz subcarrier and the variable signal it carries are affected by the velocity of the aircraft, the phase of the variable signal is changed, but by exactly the same amount than the reference signal, their difference remains constant, the bearing calculation is not affected.
Conclusion
The velocity of the aircraft influences the phase of both the reference and the variable signal, including in the DVOR and for the same reasons than in the CVOR. As only their difference is meaningful this doesn't change the resulting bearing calculation.

If by chance you wanted to dig deeper into VOR: There is more.


text:
Why are acoustic power loss never taken in account?
At university (I did mechanical engineering) I attended several courses in which energy balance was considered (e.g. thermal machines, electric machines, CFD...).
Each time a machine efficiency was investigated the loss terms taken in consideration were relative to various kinds of mechanical friction, thermal loss, hysteresis... but no term ever made reference to noise. Still some machines do produce a relevant amount of noise (e.g. fans, rotating machinery...), which should mean a waste of mechanical energy to the surrounding environment. So why is this never taken in consideration in theory?
Is it just because the loss fraction is negligible? If so, aren't there any applications for which this does not hold? And furthermore, does anyone know of a model used to quantify such losses?

An interesting topic.  One might categorize the noises into that which originates from the power source and that which eminates from the application.  Indeed, the sound from prop tips breaking the sound barrier is considered wasteful, as is noise from helicopter rotor blade interference.  Noise could indicate conditions such as higher friction (in the engine) or higher drag, but sound waves (we hear) are not as energetic as light waves or x-rays.

Did you ever ask one of your professors? They usually love when someone asks a good question...

Didn't come to mind at the time

Not relevant to aviation, but it does make a difference at the microscale. If you have a vibrating beam maybe 100 micrometers long, acoustic power loss is THE dominant source of energy loss.

Acoustic power density is too low to matter, even for very loud sustained sounds.

The roar of a train engine or the whine of a pneumatic drill ... is
about a hundredth of a watt per square meter.

-- https://engineering.mit.edu/engage/ask-an-engineer/can-sound-be-converted-to-useful-energy/
It's also been said that for a cup of room temperature coffee to reach the boiling point, assuming perfect energy transfer from the acoustic energy of two people chatting there, it would take about three thousand years.

I think you're mistaken in your comparison. Energy loss is from the central point, whereas the energy you could hope to harvest is but one very small sliver of a rapidly growing sphere. Consider an incandescent light bulb vs an LED one. Neither one would power a solar cell effectively, but one is massively more efficient than the other. Similarly, as I read it the OP's question has more to do with how much more efficient a machine could be than how much we could extract from it. Of course, it's still a small amount of energy as you point out, just not for those reasons.

True, the MIT article omits the distance from the point source of the sound, but generously guessing 10 m, then the sphere's area is 420 m$^2$, so the total power is 420 mW.  For a jackhammer, never mind a locomotive, that's a fraction of a percent of its input power.


text:
What is the EGT of a turboprop engine?
I am looking for a range of temperature of the exhaust stubs of a turboprop engine, typically a P&W one.
However, I am not able to find such information on P&W's technical documentations available on the internet. On this stackexchange, the closer topic I coud find was that one on the EGT range of a jet engine.
I would expect a temperature around 500 - 600 °C, but I am not sure about it.
Many thanks in advance for any information you would have.
Cheers!

The P&W PT6, which is probably the most common turboprop/turboshaft engine in the world, has a maximum continuous EGT of ~600°C and maximum instantaneous of 760°C.

(source: EASA)
(note: the respective document for a regular PT6 doesn't list the EGT, but only the inter-turbine temperature, ITT, which is generally used to manage the PT6 engine. Since the PT6T has the same parts, just twice, the same ITT will result in the same EGT.)
Since EGT is the terminal temperature, after all the turbine stages, it's not going to drop much while going into the exhaust. Plus, consider a slight permitted overtemperature.
Generally, if you're installing it in your plane, it's best to use materials that can handle at least 760°C for 30 seconds (where the engine might still remain in the B-area, safe to fly after inspection) and 650°C continuously (might be pushed there in a OEI contingency), with 550-600°C typical service.
This is still titanium range, but calling for high-temperature alloys such as 1100, rather than basic structural Ti-6Al-4V. Any factory exhaust will be designed for appropriate temperature.

Thank you for your reply. Yes, a PT6 is the most widespread so this was the one I was thinking about.
Many thanks for sharing the EASA document, this is exactly the type of information I was looking for. Now it's time for me to run my simulation!
Also, sorry I cannot upvote your reply since I do not have enough reputation ... but it really helped me.

@KrKAlex There's the tick mark below the answer - you'll start building up your rep after clicking it. Happy to be of help.

the ITT limit is the same, and so should be the EGT  sounds confusing, you could rephrase to explain the ITT (also explain what ITT means; Inter-Turbine Temperature) is a measure for the EGT, the only thing is that a turbine is in between the ITT and the EGT, so the ITT is higher than the EGT.

@0scar, in my case I am interested in the EGT. I consider EGT as the temperature of the air at the exit of the exhaust stubs. Therefore, I assume it is significantly lower than the ITT.

@KrKAlex Yes, the ITT is up to 1090°C. Same for PT6 and PT6T (dual installation). ITT and EGT correlate almost perfectly, except for low-speed turbine wear, which gradually increases the EGT. The PT6 engine is thermally limited at the ITT stage, so EGT is more of an informational point.

@Therac Thank you for the explanation, once again.


text:
Takeoff Distance Table: Aircraft Performance
When computing the takeoff distance on a grassy runway with a 9-knot headwind, should I first do the calculations for the grassy runway (note no. 5) on my ground roll, then apply the wind corrections (note no. 4), or vice versa?
Can I have a solution from this example? Note: values are not based from the attached table

Ground roll: 1000 feet
Total distance to clear 50 feet: 1200 feet
Wind: 9 knots Headwind
Runway: Grassy

Thank you, Captains.

I'll work with a 10kt headwind, so I can simply use the 10% decrease.
If $X$ is the ground roll, you might think that 'decrease distance by 10%' means:
$X - 0.1 \, X$
And you would be correct.  However, you can also write this as (pull the $X$ out):
$(1-0.1)\, X$
or (and simplify)
$0.9 \, X$
Similarly, a 15% increase could be interpreted as:
$X + 0.15 \, X$
or
$1.15 \, X$
So, if we need to do both, I would assume that the factors need to be applied 'on top of' each other -- not based on the original ground roll.  Consequently, it doesn't matter which order we apply them...
$0.9 \times 1.15 \, X$
or
$1.15 \times 0.9 \, X$
or
$1.035 \, X$
Working with the multiplication version of each statement is easier -- in that it makes the order independence more obvious.

I appreciate your reply, sir! For the ground roll, either way will work but the problem will occur during the computation for total distance to clear 50 feet. It says the "ground roll figure" only. Im confused whether to calculate for wind (variable factor) first or the grassy runway (constant factor).

Example.

Compute for headwind first
For ground roll:
• 1000 x 0.10 = 100, 1000-100 = 900 feet new ground roll
• 900 x 0.15 = 135 feet (15% of ground roll figure)
• 900 + 135 = 1035 feet final ground roll.

For distancce to clear 50 feet:
• 1200 + 135 (15% of ground roll figure) = 1335 new distance to clear 50 feet
• 1335 x 0.10 = 133.5, 1335 - 133.5 = 1201.5 feet final distance to clear 50 feet

Compute grassy runway first:
For ground roll:
• 1000 x 0.15 = 150 (15% of the ground roll figure)
• 1000 + 150 = 1150 new ground roll
• 1150 x 0.10 = 115, 1150-115 = 1035 final ground roll

For distance to clear 50 feet:
• 1200 + 150 (15% of the ground roll figure) = 1350 feet new distance to clear 50 feet
• 1350 feet x 0.10 = 135, 1350 - 135 = 1215 feet final distance to clear 50 feet

Based from the 2 computations, the answers for distance to clear 50 feet are not the same unlike for the "final ground roll".

I would apply the headwind first (it applies to both the ground roll and the climb segment).  After headwind, you have 900 ft. ground roll and 1080ft total to 50'.  15% of 900 is 135, so add that to both numbers to take grass into account.  1035 ground roll, 1215 total to 50'.
That said, I have a friend who perished in a small light aircraft when they took off heavy, uphill, on a grass strip, flaps down, with a light tailwind (NTSB ATL05FA098).
So, I might be tempted to apply the 15% to the un-modified 1000 ft. in an abundance of caution.  12000.9+0.151000=1230ft.

So sorry to hear this @RobMcDonald.  Yes, some other variables not reflected in the POH are 1) height of grass, 2) how dry is it really?, 3) non-company-test-pilot flying, 4) non-factory-fresh optimum engine, and 5) probably not as clean & pristine of an airframe as was flight tested to create the tables, for example.  There are other factors, also. Bottom line is it's always wise to "grow the margins" when you can.


text:
Can anyone please identify this beauty?
Obviously a German experimental flying boat.

Just use Google Image search and you will find “Oertz W.6 Flugschooner”

This is an Oertz W6 Flugschoner (source) or "Flying Schooner", a 1916 tandem biplane.

The plane took off and landed well, but had problems with control in
flight, so a second pair of ailerons was soon added between the rear
wings. Formally, the design task was completed - the boat had a
slightly greater estimated range than its predecessors, but for 1917
these indicators were more than mediocre. In addition, although armed
with two machine guns, due to its clumsiness the vehicle was an
excellent target for new fighters. For these reasons, the boat did not
find use in the fleet and was dismantled soon after testing.

source
 (source)

Thank you very much.


text:
What is the fastest fixed landing gear airplane?
Interested in knowing what the fastest fixed gear airplane is and the performance of such aircraft.

Someone has voted to close this question as low quality. That is currently true because this question needs a lot more detail and specificity on what they want. Especially an age range.
I put the answer I was able to find but perhaps it's not the best suited for this question.

Perhaps the fastest fixed-gear aircraft was the Lockheed XFV. It was  powered by a 5,332 hp (3,976 kW) Allison YT40-A-6 turboprop engine driving three-bladed contra-rotating propellers, and had a top speed of 580mph (500 kn).
 source
It has tiny wheels on it's tailfin, and was intended to take off and land vertically.
More conventionally, the WW2 German Junkers Ju 87 Stuka is said to have been able to dive at over 400mph.
 source
Diving at this speed was obviously part of its operational envelope. However, in level flight their top speed was only a little over 230mph.

"And if you think that looks strange ..." https://en.wikipedia.org/wiki/SNECMA_Coléoptère

Perhaps not what the OP was thinking of, but the Schneider Trophy was run at times from 1913 to 1931, with the fastest finish at 340 mph.
Briefly looking over this list, the Macchi M.C.72 (another seaplane) appears to be the last fixed gear record holder.

That's very interesting, wasn't expecting that. Now I have two more questions lol, are floats considered "landing gear" and does floats provide less drag than tires?...posting both as separate post....

For contemporary planes, a Google search gives these results.

Cessna Corvalis TTx (Cessna 400)

It has a cruise speed of 235 knots true airspeed at 25k feet which is also listed as the top speed for some reason.
Performance of this plane -

Rate of climb: 1,400 ft/min
Max Speed (85% at 25,000 ft): 235 kts
Economy Cruise Speed (55% at 25,000 ft): 208 kts
Range at Max Cruise Speed (85% at 25,000 ft): 825 nm
Range at Economy Cruise Speed (55% at 25,000 ft): 1,250 nm
Service ceiling: 25,000 ft (7,600 m)

Not the best source for proving that this is the fastest fixed gear propeller plane but there's many other links that are saying the same.
(Source claiming it is the fastest)
(Performance figures)


text:
Would it make sense to test the performance and handling of a prototype aircraft by mounting a free moving mock up on a track (like a rocket sled)?
https://en.wikipedia.org/wiki/Rocket_sled
When an aircraft is designed there is no way to find out if the maximum cruise speed is achievable with the chosen engine + wing + fuselage combination, and at what fuel flow.
Would it make sense to secure a section of high speed rail ( upto 320 kmh at least) to test full scale non flying models of light aircraft to get a better idea of what speeds could be achieved?
The fuselage could be sculpted and  changed repeatedly in a short time to test various drag reducing measures and forces could be measured accurately in real time. Acceleration times to take off speed could also be measured.
Edit: It does not have to be a rocket sled, just a tracked vehicle with the full size aircraft mounted on it as it is in this case with the NASA full size wind tunnel:
https://www.nasa.gov/centers/ames/images/content/109858main_AC91-0255-76.jpg
For designers of kit planes and LSAs, full size tunnel time does not seem to be an option, I don't know. The design team do well to mount their plywood or GRP prototype with its engine attached and run in on the track, controlled remotely and with some capability for movement up and down and limited movement in roll and pitch. An on-board pilot may be an option.
To test a new propeller or a cowling, or fuselage shape, or retractable gear,  wing design even, cycle times would be shorter, I think. The time to build a load bearing aerostructure, wait for good weather, time for take-off, climb and landing, not to mention test pilot time, all these would be reduced to zero - and postponed to a later stage once the design is finalized. All that is needed is to built a mock up capable of standing up to the forces on the track (2km should be OK) and the control system as well as the engine.
A typical test cycle would be as follows:
Build mock up
Test run on track and obtain data
Perform modification (replace cowl, wings, propeller etc)
Repeat the above
Considerable time and cost would be saved on the aerostructure, pilot time, fuel cost and safety would be very much better. Handling and stall behavior also could be safely tested out.

Usually aerodynamic measurements like this are performed in a wind tunnel. it's much easier and space-efficient to accelerate the air around the object than to accelerate the object itself.

@rauberdaniel Please add that as an answer.

Can you be sure that the wind tunnel data will provide you a guarantee of maximum speed and fuel flow? If aeronautical science is advanced to that stage I am ok with it.

No, it doesn't make sense because there are better alternatives:

Computer models: fluid dynamics programs are very good at simulating airflow over a 3d model
Wind tunnel testing: In a wind tunnel the airplane model stays in the same place and air is blown over it. Smoke can be added to show vortices, and cameras can record it

There are practical problems with rocket sleds:

A rocket sled would be much harder to get video from
It would be challenging to keep a rocket sled at a completely consistent speed
Rockets only last a few seconds, you'd only get a bit of data at a time

Not to mention that a bit of experience should give you a pretty decent ballpark answer.

Atmospheric conditions on the ground and at the altitude you are expected to be in cruise speed are VERY different.
The results wouldn't be valid anyway.

Very good point!  If you've ever done low-level flying - even takeoffs and landings - you will have noticed that the plane flies differently in ground effect.


text:
Suction gauge pressure too high
What will happen to the gyroscopic instruments (heading indicator and attitude indicator) if the vacuum pressure is too high? Will they be sensitive or stable?

It means the intake filter at the other end of the air system is clogged or otherwise obstructed, or some other obstruction in the plumbing that the vacuum regulator is unable to compensate for. The high suction is an indication that the flow upstream of the tap-in for the vacuum gauge is restricted.
The effect will be that the velocity of the air jets driving the gyros will be too low, and as a result they may give inaccurate or erroneous indications, have too much precession, or maybe just tumble on you. Bottom line is vacuum above or below the green arc means unreliable indications, from the gyro speed being below specification.


text:
Philippines - What is this symbol on a world aeronautical chart mean?

Need help regarding this symbol. I've checked the legend and this symbol isn't there. Thank you

It's a depiction of a large building, large enough to be usable as a landmark for navigation. The graphic roughly represents the shape of the structure.
In this case, it seems to be a structure associated with a powerplant:

(Image from Google Earth)

FAA calls them "pictorial symbols".

I really appreciate your help. Thank you so much.


text:
Sensitivity of the gyroscopic instruments if below or above green arc
What will happen to the gyroscopic instruments (heading indicator and attitude indicator) if the vacuum pressure from the engine driven vacuum pump is too high or too low?
Will the indications be sensitive or less sensitive if below the green arc on the suction gauge?
Rigidity in space principle tells us that the faster rotation of the gyros will result to being more stable. Will the indications be less sensitive then?

The housing (aircraft) moves around the gyro.  The faster the gyro, the more stable it is.  Therefor "readings" (changes in aircraft orientation) would be more reliable with a faster gyro.

The vacuum source for spinning the gyroscope inside the indicator must remain within the green arc. If it is too slow, accuracy is lost. If it is too fast, accuracy gets better but the support bearings for the gyro rotor will experience excessive wear.

This is exactly correct, I would just add to the answer that gyros spinning above spec will function even better as gyroscopes, up until the moment when they don't (due to bearing failure).

@KennSebesta, thanks, will edit. -NN


text:
Can I fly a checkride with inop vacuum indicator and attitude indicator in a TAA plane?
I have a checkride coming up and I will be taking it in a TAA plane. The vacuum indicator and attitude indicator are both inop and marked as so, but was wondering if it is still okay to fly for a commercial checkride. Those instruments are not a part of ATOMATOFLAMES, plus I do have the attitude indicator and all of my vacuum instruments on the glass panel for something to refer to. Inop process was followed but still not sure if I can still fly with just glass panel to rely on? Would it be okay to fly for a checkride?

Take a look at the MEL.  There may be relief for an inoperative vacuum system.  These standby instruments are there in the case of a complete electrical failure.  If it is not on the MEL (or no MEL exists), take a look at the equipment list (EL), you may find that it is/is not a required piece of equipment.  If it is not required, follow the guidance in 91.213 and deactivate it.

If the airplane is airworthy and the inoperative equipment is not required for the checkride tasks, you can use it for a checkride.
ATOMATOFLAMES are all required, but keep in mind that your airplane's POH, STCs, applicable ADs, etc., can all require equipment beyond just those basics.
For instance, if you are flying a Cessna 172S, the vacuum gauge is required for day VFR flight, unless the airplane has an STC or other document changing this requirement.

Check to see if your plane has a Minimum Equipment List. If not go through the following:

Check the Type Data Certificate Sheet (can be found on the FAA's DRS online) and check any Supplemental Type Certificates
Check the POH for a Kinds of Equipment List
You've already checked 14 CFR 91.205 which is good
Check for any Airworthiness Directives

If the equipment is not required by any of the above do the following:

Discard/deactivate it
Placard it as "Inoperative"
Sign off on it in the maintenance logs
Determine if as PIC you feel comfortable flying without the inoperative equipment

You should also talk to your DPE and mention you've gone through the above steps. Make them aware the equipment is inoperative and as your examiner they might make a decision.


text:
Is it possible to determine a maximum L/D possible
Over the last couple of decades L/D ratio has increased significantly. Is it possible to determine an "upper limit" on how much more potential there is for common tube-wing aircraft to improve L/D. I am looking here at commercial Aircraft. I am aware that their is already a post regarding gliders.

If there's already a similar Q&A for gliders, it would be good to edit to make that sentence a link to it.

For a jetliner flying without doing any acrobatic manoeuvres, $L$ equals weight for most (if not all) of the flight. That means that the only ways to improve $L/D$ is by reducing $D$.
At subsonic speed, drag is basically given by the sum of two terms:

induced drag, mainly drag due to lift;
and parasite drag, mainly due to skin-friction.

Induced drag can be reduced increasing wing span while skin-friction can be reduced reducing... well the skin i.e. the external surface of the aircraft and improving its smoothness.
These tricks have obviously limitations:

bigger wing span means more structure and weight and is anyway limited by space availability in airports;
smaller external surface means less space for the payload;
and however the surface smoothness is obtained, after some takeoffs and landings it is anyway gone due to dirt.

Parasitic drag includes not only skin friction drag but also form drag.

"and is anyway limited by space availability in airports" funny, that just never occurred to me!

@nanoman: I perfectly know that but I didn't want to weigh the answer down.

@Fattie: wingspan of the A380 was famously limited by that: "The optimal wingspan for this weight is about 90 m (300 ft), but airport restrictions have limited it to less than 80 m (260 ft)" (Wikipedia).

astonishing TY !

In raw physics terms there’s no theoretical upper limit.  In reality there are mechanical limits such as the strength, stiffness and durability of materials.  Also highly relevant to your question is what is considered to be a ‘common tube-wing aircraft’, which would presumably rule out high-performance designs.  So the question really comes down to how far you’re willing to stretch the definition of the term.

G load tolerance will be strongly influential in determining a L/D maximum for tube wing commercial aircraft.
Expected cruising speed will be another.
With improvements in strength and flexibility (without fatigue) advances have been made in L/D ratios, as they go hand in hand with improvements in fuel economy.  Modern airliners are in fact excellent gliders, with L/D ratios more then twice that of a Cessna 172.
This glider sports a lift to drag ratio of 70.
Higher lift to drag ratios can be had at speeds where Mach effect is not significant.  Generally, wings that can bend air without forming a transonic shock wave are most efficient.  This is usually at Mach 0.5 or less.